The low supply of petroleum based fuels in many countries has revived the interest for the development of alternative fuels or extenders for replacing or supplementing petroleum based fuels. The use of vegetable oils or blends of vegetable oils in diesel fuel appear promising for diesel engines. In particular, a large amount of test data has been accumulated burning various soybean oil/diesel fuel blends in various diesel engine configurations. The engines showing the most promise with the least modifications are those having precombustion chambers. Acceptable performance and durability have been achieved with four valve engines having centrally located precombustion chambers. However, it was found that two valve engines having a precombustion chamber located nonsymmetric or offset with respect to the main combustion chamber were susceptible to increased wear to the piston rings and the cylinder bore. Such high piston ring and cylinder bore wear has been attributed to fuel impingement on the cylinder bore due to the poorer atomization and slower burning characteristics of the vegetable oil. The partially burned fuel impinging against the cylinder bore results in high dilution of the lubricating film and heavy deposits on the piston rings and cylinder bore which lead to ring sticking, corrosion and wear.
In order to effectively burn vegetable oil or blends of vegetable oil and petroleum based fuel, it became apparent that modifications to some of the engine components would be necessary. One of the considerations in modifying the engine is that such modifications should not unduly hinder the burning of straight petroleum based diesel fuel.
The present invention is directed to overcoming one or more of the problems as set forth above.